In certain fields of application, there is a need for microwave filters of very high power. This is the case for example in the space field, where the transmit power must be particularly high and where the filters used must be effective at high power levels in order to provide a maximum transmit power. This is the case for example in direct transmission systems by satellite. The satellite must then be able to transmit with a maximum power. However, the invention is applicable in any other field in which high-power operation is required.
When a waveguide is used in a vacuum (for space applications) and in the case of high-power waveguides, it is possible to initiate an electron avalanche, called a multipactor effect, in certain zones of the waveguide.
This multipactor effect is caused by a concentration of the electromagnetic field which tears electrons out of the walls of the waveguide. The electrons are then accelerated toward the opposite wall of the waveguide. The impact of these electrons on the latter wall causes in turn electrons to be torn therefrom, and so on. An electron avalanche phenomenon thus occurs, which degrades the electrical performance of the waveguide and may lead to it being destroyed.
This phenomenon therefore occurs notably in the space field in which the waveguides operate in a vacuum in the absence of air molecules.
The multipactor power level is the maximum power at which a component can be used without initiating the multipactor effect. This threshold power can be calculated between two parallel plates from the following equation:P=(1/VMF2)×(Vmulti2/2Z0)where                the multipactor threshold voltage (Vmulti) is dependent on the type of equipment used to manufacture the waveguide, but this voltage is always proportional to the product of the frequency multiplied by the critical distance between the plates (f×d);        the VMF (voltage magnification factor) is the ratio of the voltage at the point of calculation and the input voltage of the component. This VMF increases with the field concentration between the two plates at the calculation point; and        the impedance (Z0) depends on the standard of waveguide used and on the working frequency (normally fixed by the application).        
To reduce this multipactor effect, it is possible either to move the walls of the waveguide further apart in order to increase the Vmulti or to reduce the electric field concentration in order to reduce the VMF.
Both these solutions pose problems. If moving the walls of the waveguide further apart is envisioned, the operating frequency range is reduced and the device will have difficulties matching the waveguide for all frequencies in the operating range.
To reduce the concentration of the electric field at the critical point, it is necessary to modify the topology of the devices, or even, in the case of filters, to change the type of filter.
The object of the invention is to solve these problems and to provide a microwave waveguide and microwave filters in which the multipactor power level has been notably increased.